The latest issue of the Rio Grande Modeling & Historical Society's Prospector magazine has a reprint from Railway Age Magazine about water tanks on the D&RGW as well as tank car gallery article that I wrote.
[www.drgw.org]
The D&RGW began to paint tanks with the buff color and the RG/MT herald in the late 1930s. I have photos of the Jack's Cabin tank in 35 when it was red and in 37 when it was buff. Some of the smaller tanks like the Villa Grove tank were done in gray with black lettering, while the small Jack's Cabin tank built to replace the original in the late 40s was painted red.